Vita faulty battery/gauge

Hi guys i am having a really annoying problem with my Vita. After fully charging my battery I will get the battery low warning after a few minutes play. I go to the home screen and sure enough its on red. It will then jump back to green/full.

This will continue untill the battery is genuinly drained, sometimes also the Vita will display the empty battery symbol and go into sleep mode . Pressing the home button will wake the Vita up and the battery will show as full again.

I have tried draining the battery fully and doing a full recharge yet the same thing happens. Its nearly out of warrenty and sods law I purchased it from HMV . Does anyone have any ideas on how to fix this or come across this problem at all?
Google isnt turning up anything.

Are you sure it's charging properly? I thought I had an issue with mine, but then realised that the chargr cable had come loose so hadn't charged the Vita properly, despite me leaving it to charge overnight.

Have you tried completely switching it off? Hold the power button down for 3-4 seconds and select Power Off and then try to turn on again. If it won't turn on, plug in the charger and ensure the Home button glows orange.

Yea i have tried powering it off as well. Ive got a few weeks left on my warrenty but its with HMV . Do you know if they would have to honour it ? Or am I at the back of the que with the shafted gift card lads?